His palfrey was as broun as is a berye.

Meaning

(= His riding-horse was as brown as a berry.)

A ‘palfrey’ was a horse for riding; it didn’t refer to a particular breed.

So whaddya think of the Monk? James Winny, in the Cambridge edition of The General Prologue, suggests that while Chaucer makes it clear that the Monk was a total failure in his vocation, Chaucer admired his vitality and merry attitude. It’s worth thinking about just how ironic Chaucer is being.